Ducted vs Recirculating Fume Hoods

A fume hood is a very common piece of equipment in any laboratory setting – most laboratories have one. A useful tool, fume hoods allow lab workers to conduct experiments or activities with dangerous chemicals in safety. Using a fume hood is like using an advanced kitchen rangehood.

With more and more innovations of late with fume hoods, many get confused with which one to choose. Westlab explains the differences.

Ducted Fume Hood 

Ducted fume hoods are the most common, especially in laboratories dealing with heavy-duty or harmful chemicals. Large professional-grade fume hoods often have services such as electricity, gases such as nitrogen, CO2, Oxygen or natural gas.

The main character in question, however, is the duct. A ducted fume hood has an opening at the top, where fume extraction occurs with the help of a powerful exhaust fan at the end of the line.

Ductwork in the ceiling is used to transport the fumes into the air outside, which is why often laboratories can be picked from a distance by the extensive ductwork coming out of the roof.  
In a fume hood like this, constant levels of vacuum must be achieved to be effective, meaning all gases are always moving upwards through the ductwork, and not circulating inside the apparatus.

Pros:

• Can work with heavy-duty materials
• Reliable
• HVAC system ensures no nasty materials are recirculated back into the building

Cons:

• Not modular or flexible
• HVAC system means that maintenance or need of repairs may render it useless
• Installation costs

Ductless Fume Hood

A ductless fume hood is a far more versatile and cost-efficient option, however not suited to harsher chemicals.

As the name suggests, its main difference is the absence of ductwork. Also known as a recirculating fume hood, ductless systems use activated HEPA carbon filters in place of a large ducted outlet. Using fans to create the perfect levels of vacuum in the fume hood, the air is purified and released back into the lab as clean, fresh air.

The main advantage of this system is that it does not require an HVAC system in the building, and does not attract the large costs of building ductwork and HVAC systems into the structure, an operation which is neither versatile, agile or cost-efficient. A ductless fume hood can be easily transported on castors, and simply plugged into a wall socket for easy use. This makes it an ideal future-proofing option for labs, where it can be incorporated with modular furniture for endless space optimization.

Pros:

• Cost-effective installation
• Flexibility and Modularity
• Convenience 

Cons:

• Not ideal for heavy chemicals (limited range of compatibility)
• Regular filter maintenance costs
• Can be unreliable

Which one should I purchase?

There are many criteria to consider when choosing a fume hood for your laboratory, and many get confused with which one to choose. 

Here are a few things to consider.